Changes in Polycyclic Aromatic Hydrocarbons (PAHs) and Soil Biological Parameters in a Revegetated Coal Mine Spoil

A review on environmental contamination of petroleum hydrocarbons, its effects and remediation approaches

Oil leakage into soil is a major environmental concern, affecting its physical, chemical, biological, and geotechnical properties, which threatens soil fertility. Remediating contaminated sites helps mitigate risks to human health, the environment, and the economy, while also enabling land reuse for development or agriculture. Petroleum spills generally occur during production, processing, transportation, and storage. This review discusses the impact of hydrocarbon contamination on soil and its surrounding environment and examines various remediation techniques, including physical-chemical methods (soil excavation, soil washing, soil vapor extraction, thermal treatment, and chemical oxidation), biological methods (bioremediation and phytoremediation), nanotechnology-based approaches, and integrated methods. The effectiveness, limitations, and applicability of these techniques are critically analyzed, providing a comprehensive framework for managing soil contamination by petroleum hydrocarbons.

Modeling land-degradation vulnerability in coal-mined environs through geospatial and AHP techniques: potential strategies for eco-restoration

Coal is the most important and abundant source of energy in India, where 66% of the thermal power is generated from the combustion of coal. Therefore, understanding how coal-mining activities increase land-degradation risks and vulnerabilities in different land uses is essential to devise site-specific restoration plans for complementing the national targets of land degradation neutrality (LDN). This study was carried out in the Chirimiri coal-mining region of Chhattisgarh, India, employing geospatial methods. The Landsat Thematic Mapper (TM) and Operational Land Imager (OLI) data corresponding to 2000, 2010, and 2020 were digitally classified using maximum-likelihood algorithm in ERDAS IMAGINE and ArcGIS platforms. Spatio-temporal satellite data analysis revealed that an area encompassing ~ 112 km2 (48.9%) of forests and 6.63 km2 (37.6%) of waterbodies was lost due to the expanse of mining between 2000 and 2020. Consequently, the degraded land and built-up areas rapidly expanded during the same period accounting for a net increase of 101.1 km2 (47%) and 9.13 km2 (322%). The mining disturbances degenerated the soil health, drastically reducing soil pH, soil organic carbon (SOC), and available nitrogen (N) in the mined area exacerbating the region's vulnerability to degraded lands. Land Degradation Vulnerability Index (LDVI) map shows that mined area was highly vulnerable, followed by barren wasteland, agriculture, and forest area, while destructive mining and other associated activities in the past 20 years made 52% of the landscape vulnerable. The study discusses the implications of effective eco-restoration for minimizing the land degradation processes and building resilient ecosystems for mitigating land degradation in coal-mined landscapes.

Exploring the Potential of Microbial Coalbed Methane for Sustainable Energy Development

By allowing coal to be converted by microorganisms into products like methane, hydrogen, methanol, ethanol, and other products, current coal deposits can be used effectively, cleanly, and sustainably. The intricacies of in situ microbial coal degradation must be understood in order to develop innovative energy production strategies and economically viable industrial microbial mining. This review covers various forms of conversion (such as the use of MECoM, which converts coal into hydrogen), stresses, and in situ use. There is ongoing discussion regarding the effectiveness of field-scale pilot testing when translated to commercial production. Assessing the applicability and long-term viability of MECoM technology will require addressing these knowledge gaps. Developing suitable nutrition plans and utilizing lab-generated data in the field are examples of this. Also, we recommend directions for future study to maximize methane production from coal. Microbial coal conversion technology needs to be successful in order to be resolved and to be a viable, sustainable energy source.

Responses of soil bacterial community structure to different artificially restored forests in open-pit coal mine dumps on the loess plateau, China

Artificial vegetation restoration is an effective method for improving soil quality. In areas experiencing coal mine subsidence, the microbial community is essential for reconstructing the ecological balance of the soil. Studies are needed to examine how soil microbial community structure respond to different artificial forest restoration types and ages, especially over long-term periods. Therefore, in this study, 10, 20, and 30-year trials were chosen with two restoration types: Pinus tabuliformis (PT) and Ulmus pumila (UP). The objective was to determine how various types and ages of forest restoration affect the structure of soil bacterial communities, as well as the soil environmental factors driving these changes. The results showed that artificial 30-year restoration for both PT and UP can improve soil physical and chemical properties more than restoration after 10 and 20 years. The soil bacterial community structure remarkably differed among the different forest types and restoration ages. The bacterial diversity was higher in UP than in PT; the alpha diversity at longer restoration years (30 and 20) was significantly higher than at 10 years for both PT and UP. Moreover, soil nutrients and pH were the primary soil environmental factors driving bacterial community structure in the PT and UP. Finally, the integrated fertility index (IFI) at 30 years of restoration was considerably higher for PT and UP, and thus, is more beneficial to the restoration of soil after coal mining. Our findings are useful for studying improvement in soil quality and the restoration of the ecological environment in mining areas.

Characteristics of organic pollutants and their effects on the microbial composition and activity in the industrial soils of Pearl River Delta, China

To investigate the interaction between organic pollutants and soil microorganisms, industrial soils were collected from Pearl River Delta region of China for determining semi-volatile organic pollutants, the community structure and activity of microorganisms. The results showed that polycyclic aromatic hydrocarbons (PAHs) (63.3-4956 μg kg^-1) and phthalate esters (PAEs) (272-65,837 μg kg^-1) were main organic pollutants in the research area soils. Chemical manufacturing industry and plastics manufacturing industry contributed greatly to PAH pollution and PAE pollution, respectively. Organic pollutants changed the biomass of microorganisms. In most industrial soils, the biomass of actinomycetes was the highest in the industrial soils, followed by G^- bacteria, G⁺ bacteria and fungi. The exception was that the biomass of fungi in the soil near chemical manufacturing industry was greater than that of G⁺ bacteria. The soil microbial biomass (including soil microbial biomass carbon, soil microbial biomass nitrogen, the biomass of actinomycetes, bacteria, and fungi) and soil enzyme activities (sucrase and urease) positively correlated with the organic pollutant residues, and the microbial species diversity and microbial species abundance decreased with organic pollutant residues increasing. Based on the correlation analysis, the urease activity, actinomycetes biomass, and fungi biomass were appropriate biological indicators for evaluating the stress of organic pollutants. Our research provides a new perspective for understanding the soil biological response in industrial soils.

Effect of partially hydrolyzed polyacrylamide (HPAM) on the bacterial communities of wetland rhizosphere soils and their efficiency in HPAM and alkane degradation

The effect of partially hydrolyzed polyacrylamide (HPAM) on structure and function of rhizosphere soil bacterial communities in constructed wetlands has been largely underinvestigated. In this study, we compare the effect of 250, 500, and 1000 mg/L of HPAM on bacterial community composition of Phragmites australis associated rhizosphere soils in an experimental wetland using MiSeq amplicon sequencing. Rhizosphere soils from the HPAM-free and the 500-mg/L-exposed treatments were used for laboratory experiments to further investigate the effect of HPAM on the soil's degradation and respiration activities. Soils treated with HPAM showed differences in bacterial communities with the dominance of Proteobacteria and the enrichment of potential hydrocarbon and HPAM-degrading bacteria. CO₂ generation was higher in the HPAM-free soils than in the HPAM pre-exposed soil, with a noticeable increase in both soils when oil was added. The addition of HPAM at different concentrations had a more pronounced effect on CO₂ evolution in the HPAM-pre-exposed soil. Soils were able to degrade between 37 ± 18.0 and 66 ± 6.7% of C₁₀ to C₃₀ alkanes after 28 days, except in the case of HPAM-pre-exposed soil treated with 500 mg/L where degradation reached 92 ± 4.3%. Both soils reduced HPAM concentration by 60 ± 15% of the initial amount in the 500 mg/L treatment, but by only ≤ 21 ± 7% in the 250-mg/L and 1000-mg/L treatments. In conclusion, the rhizosphere soils demonstrated the ability to adapt and retain their ability to degrade hydrocarbon in the presence of HPAM.

Exogenous melatonin reduces water deficit-induced oxidative stress and improves growth performance of Althaea rosea grown on coal mine spoils

Coal mining activities are responsible for significant land degradation and often long-term irreversible effects on ecosystem functioning. To better understand how coal mined sites could be re-vegetated and ecosystem functioning restored, we address the role of the signalling hormone melatonin, which controls plant growth and development under adverse environmental conditions. We assessed the effects of exogenous melatonin on the plant species Althaea rosea by measuring morphological growth attributes, photosynthetic efficiency, reactive oxygen species (ROS)-induced oxidative damage and antioxidant defence developed by the seedlings when grown on coal-mined spoils under various water regimes. Water deficit and negative effects of coal mine spoils significantly decreased morphological growth attributes (i.e. plant height, root length and dry biomass), gas-exchange traits (i.e. net photosynthesis rate, inter intercellular concentration of CO₂, transpiration rate, stomatal conductance and water use efficiency) and photosynthetic pigments (chlorophyll and carotenoid contents) by increasing the ROS-induce oxidative damage and decreasing antioxidant enzyme activities of A. rosea seedlings. However, melatonin applications increased photosynthetic performance and antioxidant enzyme activities and decreased hydrogen peroxide and malondialdehyde contents and ultimately improved growth performance of A. rosea in coal-mined spoils. Overall, our findings show how the application of optimum water (63.0 %field capacity equivalent to 1.67 mm day^-1) and melatonin (153.0 μM dose) significantly improves the re-vegetation of coal-mined spoils with A. rosea. Our study provides new insight into melatonin-mediated water stress tolerance in A. rosea grown on coal-mined spoils, and this strategy could be implemented in re-vegetation programmes of coal mine-degraded areas under arid and semiarid conditions of the north-western part of China and perhaps across other arid areas worldwide.

Revegetation of coal mine degraded arid areas: The role of a native woody species under optimum water and nutrient resources

Ecological restoration of coal mine degraded soils across arid and semi-arid environments worldwide remains particularly challenging. We used a combination of greenhouse and field experiments to assess the potential role of a woody species, Ulmus pumila, in the restoration of degraded soils associated with coal-mining activities in the northwest China. We investigated how various combinations of water-nitrogen-phosphorus (W-N-P) resources affect multiple growth parameters in U. pumila. We found that several plant growth traits significantly improved with W-N applications, regardless of P inputs. Moderate-to-highest W-N-P doses increased net photosynthesis and transpiration rates, water use efficiency, stomatal conductance, chlorophyll and carotenoid contents under greenhouse conditions. A combination of high W together with low N-P applications led to high relative water content and net photosynthetic rates under field conditions. Increasing of N-P doses under W-shortage condition, aided U. pumila to enhance osmotic adjustments by increasing contents of proline and soluble sugar and also boost the activity of superoxide dismutase, peroxidase and catalase in leaf tissues to reduce accumulation of reactive oxygen species and malondialdehyde content in all conditions of greenhouse and field. Our study is the first to assess the optimum W-N-P resources in U. pumila and demonstrate that optimum growth performance could be obtained under W supplements corresponding to 90 mm year-1, N and P at 110 and 45 kg ha-1, respectively, under field condition. These findings can have far reaching implications for vegetation restoration of degraded areas associated with coal-mining activities across arid and semi-arid regions worldwide.

Plant-Soil Feedbacks for the Restoration of Degraded Mine Lands: A Review

Much effort has been made to remediate the degraded mine lands that bring severe impacts to the natural environments. However, it remains unclear what drives the recovery of biodiversity and ecosystem functions, making the restoration of these fragile ecosystems a big challenge. The interactions among plant species, soil communities, and abiotic conditions, i.e., plant-soil feedbacks (PSFs), significantly influence vegetation development, plant community structure, and ultimately regulate the recovery of ecosystem multi-functionality. Here, we present a conceptual framework concerning PSFs patterns and potential mechanisms in degraded mine lands. Different from healthy ecosystems, mine lands are generally featured with harsh physical and chemical properties, which may have different PSFs and should be considered during the restoration. Usually, pioneer plants colonized in the mine lands can adapt to the stressful environment by forming tolerant functional traits and gathering specific soil microbial communities. Understanding the mechanisms of PSFs would enhance our ability to predict and alter both the composition of above- and below-ground communities, and improve the recovery of ecosystem functions in degraded mine lands. Finally, we put forward some challenges of the current PSFs study and discuss avenues for further research in the ecological restoration of degraded mine lands.

The Modulation of Water, Nitrogen, and Phosphorous Supply for Growth Optimization of the Evergreen Shrubs Ammopiptanthus mongolicus for Revegetation Purpose

Surface mining is a critical anthropogenic activity that significantly alters the ecosystem. Revegetation practices are largely utilized to compensate for these detrimental impacts of surface mining. In this study, we investigated the effects of five water (W) regimes [W₄₀: 40%, W₄₈: 48%, W₆₀: 60%, W₇₂: 72%, and W₈₀: 80% of field capacity (FC)], five nitrogen (N) (N₀: 0, N₂₄: 24, N₆₀: 60, N₉₆: 96, and N₁₂₀: 120 mg kg^-1 soil), and five phosphorus (P) fertilizer doses (P₀: 0, P₃₆: 36, P₉₀: 90, P₁₄₄: 144, and P₁₈₀: 180 mg kg^-1 soil) on morpho-physiological and biochemical parameters of Ammopiptanthus mongolicus plants to assess the capability of this species to be used for restoration purposes. The results showed that under low W-N resources, A. mongolicus exhibited poor growth performance (i.e., reduced plant height, stem diameter, and dry biomass) in coal-degraded spoils, indicating that A. mongolicus exhibited successful adaptive mechanisms by reducing its biomass production to survive long in environmental stress conditions. Compared with control, moderate to high W and N-P application rates greatly enhanced the net photosynthesis rates, transpiration rates, water-use efficiency, chlorophyll (Chl) a, Chl b, total Chl, and carotenoid contents. Under low-W content, the N-P fertilization enhanced the contents of proline and soluble sugar, as well as the activities of superoxide dismutase, catalase, and peroxidase in leaf tissues, reducing the oxidative stress. Changes in plant growth and metabolism in W-shortage conditions supplied with N-P fertilization may be an adaptive strategy that is essential for its conservation and restoration in the desert ecosystem. The best growth performance was observed in plants under W supplements corresponding to 70% of FC and N and P doses of 33 and 36 mg kg^-1 soil, respectively. Our results provide useful information for revegetation and ecological restoration in coal-degraded and arid-degraded lands in the world using endangered species A. mongolicus.

Can biochar reclaim coal mine spoil?

Surface coal mining activities completely destroy vegetation cover, soil and biodiversity. The aftermaths include huge coal mine spoil dumps, changed topography, drainage and landscape, deteriorated aesthetics and increased pollution load. These coal mine spoils are characterised by high rock fragments, extremely low water holding capacity, compacted and high bulk density, lack of organic carbon and plant nutrients, low cation exchange capacity, acidic pH and toxic metal contamination, which poses difficulties in reclamation. An array of studies has been focused on the sustainable use of biochar for restoration of degraded agricultural soil by improving the soil physicochemical, nutritional and biological properties. Although a volume of studies has been done on biochar application, its specialised application in reclamation of coal mine spoils is still atypical, also a systematic review on the mechanism by which biochar amends the mine spoil is lacking. This review focuses on i) factors affecting the biochar properties, ii) the mechanism involved in altering the physical, chemical and biological properties by biochar, (iii) remediation of potentially toxic elements in soil and restoration of degraded land using biochar, and, iv) highlighting the important aspects to be considered while using biochar for reclamation of coal mine spoil. Biochar prepared at 450 °C from a lignocellulosic rich biomass can be an alternative for reclamation for coal mine spoil. Review also suggested suitable methodologies for bulk production, application and economics of biochar in coal mine spoil reclamation.

Fine-tuning of soil water and nutrient fertilizer levels for the ecological restoration of coal-mined spoils using Elaeagnus angustifolia

Coal mining activities remain of great environmental concern because of several negative impacts on soil ecosystems. Appropriate revegetation interventions of coal-spoiled lands can provide environmental management solutions to restore soil degraded ecosystems. The present study addressed the potential of the pioneer woody species, Elaeagnus angustifolia, in the restoration of coal-mined spoils under a range of different water (W) levels and nitrogen (N) and phosphorus (P) applications. Our results show how moderate applications of N (N₆₀ = 60 mg N kg^-1 soil) and P (P₉₀ = 90 mg P kg^-1 soil) fertilizers led either to maximum or minimum growth performance of E. angustifolia depending on whether W was applied at very high (W₈₀ = 80% field capacity) or very low (W₄₀ = 40% field capacity) levels suggesting that W was the main limiting factor for plant growth. Very low-W regime (W₄₀N₆₀P₉₀) also caused significant reduction of photosynthetic parameters, including net photosynthetic rate, transpiration rate and water use efficiency. The combination of high W-N doses with low P doses (W₇₀N₉₆P₃₆) positively influenced gas-exchange parameters, chlorophyll and carotenoid contents. Seedlings treated with low-W and -N doses (W₅₀N₂₄P₁₄₄) showed highest increases in malondialdehyde content and lowest levels of relative water content (RWC). Decreases in malondialdehyde content and increases in RWC were observed following a gradual increment of W and N doses, indicating that high W and N doses contributed to drought tolerance of E. angustifolia by protecting cell membranes and increasing water status. Low-W and -N applications considerably increased the activities of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) and the contents of proline and soluble sugars, suggesting that E. angustifolia developed defensive strategies to avoid damage induced by water scarcity. Results from heatmap and principal component analyses confirmed that W and N were the main clustering factors, and both N and P performed well at high-W dose. The optimum growth performance of E. angustifolia was found under a combination of W level at 66.0% of field capacity, N dose of 74.0 mg kg^-1 soil, and P dose of 36.0 mg kg^-1 soil. Our findings demonstrate how optimum growth performance of E. angustifolia can be achieved by fine-tuning doses of W, N, and P resources, and how this in turn could greatly support the ecological restoration of coal-mined degraded environments.

Improvement of growth performance of Amorpha fruticosa under contrasting regime of water and fertilizer in coal-contaminated spoils using response surface methodology

BACKGROUND

Water availability and nutrient-status of soils play crucial roles in seedling establishment and plant survival in coal-spoiled areas worldwide. Restoration of spoils pertains to the application of proper doses of nutrients and water, and selection of particular plant species for efficient revegetation. This study aimed at examining the potential effects of different combinations of soil-water and fertilizers (nitrogen, N and phosphorus, P) on morpho-physiological and biochemical attributes of Amorpha fruticosa grown in coal-mined spoils. Three factors five-level central-composite-design with optimization technique response surface methodology (rsm) was used to optimize water irrigation and fertilizer application strategies.

RESULTS

Our results revealed a strong correlation between experimental data and predicted values developed from the rsm model. The best responses of A. fruticosa in terms of plant height, stem diameter, root length, and dry biomass were observed under a high-water regime. Low-water regime caused a notable reduction in growth-associated parameters, and fertilization with either N or P did not show positive effects on those parameters, indicating that soil-water was the most influential factor for growth performance. Leaf water potential, gas-exchange parameters, and chlorophyll content significantly increased under high levels of soil-water, N and P, suggesting a synergistic effect of these factors for the improvement of photosynthesis-related parameters. At low soil-water contents and N-P fertilizer application levels, enhanced accumulation of malondialdehyde and proline indicated that A. fruticosa suffered from oxidative and osmotic stresses. Amorpha fruticosa also responded to oxidative stress by accelerating the activities of superoxide dismutase, catalase, and peroxidase. The effects of both fertilizers relied on soil-water, and fertilization was most effective under well-watered conditions. The maximum growth of A. fruticosa was observed under the combination of soil-water, N-dose and P-dose at 76% field capacity, 52.0 mg kg^- 1 and 49.0 mg kg^- 1, respectively.

CONCLUSION

Our results demonstrate that rsm effectively designed appropriate doses of water and N-P fertilizer to restore coal-spoiled soils. Furthermore, A. fruticosa responded to low-water and fertilizer-shortage by upregulating defensive mechanism to avoid damage induced by such deficiencies. Finally, our findings provide effective strategies for revegetation of coal-contaminated spoils with A. fruticosa using appropriate doses of water and N-P fertilizers.

Effects of corn straw on dissipation of polycyclic aromatic hydrocarbons and potential application of backpropagation artificial neural network prediction model for PAHs bioremediation

In order to provide a viable option for remediation of PAHs-contaminated soils, a greenhouse experiment was conducted to assess the effect of corn straw amendment (1%, 2%, 4% or 6%, w/w) on dissipation of aged polycyclic aromatic hydrocarbons (PAHs) in contaminated soils. Backpropagation artificial neural network (BP-ANN) was applied to model the relationships between soil properties and PAHs concentration in soils. The removal rate of PAHs, enzyme activity (catalase and dehydrogenase), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) in soils were investigated to evaluate the dissipation of PAHs under different ratio of corn straw amendment. The present study showed that corn straw amendment apparently accelerated the dissipation of PAHs after incubation of 112 days, especially under 4% and 6% treatments. Compared with non-amended soil, corn straw amendment significantly (p < 0.05) increased the removal rate of low molecular weight (LMW) PAHs and significantly (p < 0.05) enhanced the dissipation of high molecular weight (HMW) PAHs only under 6% treatment. Moreover, corn straw amendment increased activities of catalase and dehydrogenase, concentrations of DOC and MBC in soils, which are beneficial to the degradation of PAHs in soils. The performance of the BP-ANN model was assessed through the root mean square error (RMSE) and determination coefficient (R²). The results indicated that BP-ANN model could provide satisfactory prediction of PAHs concentration in soils during incubation period at R² and RMSE values of 0.948, 187.4 μg kg^-1, respectively. The results indicated that high amendment of corn straw was a potential option for remediation of PAHs-contaminated soils and that the BP-ANN model could successfully provide prompt prediction of PAHs concentration in soils.

Rhizoremediation of petroleum hydrocarbons: a model system for plant microbiome manipulation

Phytoremediation is a green and sustainable alternative to physico-chemical methods for contaminated soil remediation. One of the flavours of phytoremediation is rhizoremediation, where plant roots stimulate soil microbes to degrade organic contaminants. This approach is particularly interesting as it takes advantage of naturally evolved interaction mechanisms between plant and microorganisms and often results in a complete mineralization of the contaminants (i.e. transformation to water and CO2 ). However, many biotic and abiotic factors influence the outcome of this interaction, resulting in variable efficiency of the remediation process. The difficulty to predict precisely the timeframe associated with rhizoremediation leads to low adoption rates of this green technology. Here, we review recent literature related to rhizoremediation, with a particular focus on soil organisms. We then expand on the potential of rhizoremediation to be a model plant-microbe interaction system for microbiome manipulation studies.

Influence of different revegetation choices on plant community and soil development nine years after initial planting on a reclaimed coal gob pile in the Shanxi mining area, China

In order to identify suitable pioneer plant species for future revegetation of coal gob piles, a field survey was conducted to assess the success of different revegetation species and their influence on soil development nine years after initial planting on a reclaimed coal gob pile in the Yangquan mining area of Shanxi province, China. Data were analyzed using a quantitative classification method (TWINSPAN), ordination techniques (DCA and DCCA), Principal Component Analysis (PCA) and a geo-accumulation index (Igeo). The results revealed that the low levels of soil moisture and available N were the major limiting factors affecting plant community development on the coal gob pile, not metal toxicity. The plant communities that developed had significantly improved the topsoil (0-10cm) quality on the reclaimed coal gob pile nine years after initial planting (p<0.05), but the degree of improvement varied greatly with different planted species. Revegetation types comprised of the planted leguminous species, Medicago sativa and Amorpha fruticosa, and the non-leguminous species, Populus tomentosa and Salix babylonica had the best ecological restoration effects on the reclaimed coal gob pile. Revegetation using these species is therefore recommended for future reclamation of abandoned coal gob piles in this region.